Samarium cation (Sm+) reactions with H2, D2, and HD: SmH+ bond energy and mechanistic insights from guided ion beam and theoretical studies.

Guided ion beam tandem mass spectrometry is used to study the reaction of the lanthanide samarium cation (Sm+) with H2 and its isotopologues (HD and D2) as a function of collision energy. Modeling the resulting energy dependent product ion cross sections from these endothermic reactions yields 2.03 ± 0.06 eV (two standard deviations) for the 0 K bond dissociation energy of SmH+. Quantum chemical calculations are performed to determine stabilities of the ground and low-energy states of SmH+ for comparison with the experimentally measured thermochemistry. The calculations generally overestimate the SmH+ bond energy, but a better agreement between experiment and theory is achieved after correcting for spin-orbit energy contributions, with coupled-cluster with single, double and perturbative triple excitations/complete basis set [CCSD(T)/CBS] results reproducing the experiment well. In the HD reaction, the SmH+ product is observed to be favored over the SmD+ by about a factor of three, indicating that the reaction proceeds via a direct mechanism with short-lived intermediates. This is consistent with quantum chemical calculations of relaxed potential energy surface scans of SmH2 +, which show that there is no strongly bound dihydride intermediate. The reactivity and hydride bond energy of Sm+, which has a valence electron configuration typical of most lanthanides, are compared with previous results for the lanthanide cations La+, Gd+, and Lu+, which exhibit configurations more closely related to the group 3 metal cations, Sc+ and Y+. Periodic trends across the lanthanide series and insights into the role of the electronic configurations on hydride bond strength and reactivity with H2 are discussed.